This invention relates to a batch method for making solid-electrolyte capacitors and more particularly to such capacitors having metal loaded resin end caps.
Capacitors having end cap terminals are especially suitable for flush mounting to a printed wiring board, or the like, usually by reflow soldering thereto. An insulative layer is normally provided over a major portion of a capacitor pellet, which pellet includes a porous valve-metal core having an oxide dielectric film formed over its surfaces, a solid electrolyte over the film and a metallic counterelectrode over the solid electrolyte. A metal loaded resin paint is applied over opposite ends of the pellet and partially over the insulative layer. One paint layer contacts the counterelectrode and the other contacts a valve-metal riser wire extending from the core.
The insulative layer may be applied by dipping the pellet into a liquid resin and curing the resin. This resin is removed from the pellet in predetermined region by blotting and wiping as is described by Thompson et al in U.S. Pat. No. 4,090,288, issued May 23, 1978 and is assigned to the same assignee as the present invention. Such procedures are amenable to batch fabrication of capacitors. However, much care is needed in the dipping step to control the amount of resin that is deposited in the critical region of the pellet from which the anode riser wire extends. Also if the pellets are subsequently immersed into activating and plating electrolyte solutions the insulative coating must be free of porosity and pin holes and be impervious to such electrolytes which may seriously damage the underlying solid electrolyte and dielectric oxide film. Such damage results in higher dissipation factors, higher leakage currents and sometimes shorting of the capacitor.
It is therefore an object of this invention to provide a low-cost batch method for making solid electrolyte capacitors with a precisely defined and impervious insulative coating over which terminal caps are applied.